The invention is directed to improvements in an rpm governor for fuel injection pumps. One problem with Diesel governors in general is how to control the relatively large adjusting forces that are required in such a way that when there are slight changes in such parameters as load, rpm, temperature and the like, it is still possible to effect a small change in the travel of the quantity control member and thus to finely regulate the injection quantity. This relationship among forces means that governor elements such as rpm signal transducers are relatively large, regardless of whether they operate by hydraulic or centrifugal means, and also that the governor springs are correspondingly strong, or in other words of large dimensions.
The relationship among the forces operative in such a governor, such as that between the spring force and a centrifugal force which has a completely different characteristic, makes it necessary to match these governor elements to one another in order to approach the ideal fuel consumption charactgeristic of the engine as closely as possible. Something which still seems to be relatively simple when considered in static terms becomes impossible when considered dynamically, because the adjusting forces fed into the governor, such as for rapidly adapting the injection quantity to what is actually required under conditions of abrupt load changes, depend much more on the rpm than on the actual load. On the other hand, overly rapid adjustments of fuel guantity cause the engine to react to the increased fuel quantity, which is appropriate for a higher load, by misfiring, which results in engine bucking or seesawing. A further factor is that the fuel consumption of the engine does not increase at all linearly with the rpm; instead, it decreases again at higher rpm, which is known to necessitate an adjustment of the injection quantity. It therefore becomes particularly difficult to add further control elements in such a governor, for taking other engine parameters such as air pressure into account. Although the use of a transmission lever having arms of different length between the quantity control member and the adjusting member (U.S. Pat. No. 4,519,352) substantially reduces the adjusting forces needed to intervene in the governor, nevertheless this is achieved at the expense of a long adjusting path for the adjusting member. For instance, if a pressure box is used as the adjusting member in this known governor, then the pressure box must be of such a size, that it will have adjusting path of the required length.
Electronically controlled Diesel governors are also known, which do have the advantage of processing the actual values of the various engine parameters very accurately, via an electronic control unit, into adjusting values for the quantity control member, but also have the disadvantage that if the electrical system fails, the entire fuel injection system is shut down as well, and on the other hand that the electrical output variables of the control unit must be converted into correspondingly large mechanical adjusting forces in order to actuate the quantity control member. A consequence of the latter disadvantage, particularly, is extraordinarily large and expensive rpm governors.
For this reason, rpm governors for injection pumps have been developed in which elastic governor elements such as springs are acted upon via electrical final control elements, so as to thereby vary the governor variable that sets the standard for the adjustment of the quantity control member (Japanese utility model application No. 59 939/81). However, these known governors have the disadvantage that an adjustment can be made in only one governor element at a time, using an associated electrical adjusting member.